Overview
The MEL Scripts group of attributes provides the ability to execute MEL scripts at certain stages during the rendering process. This opens up the possibility of doing whatever tweaks required at these stages. Since 3Delight comes with a set of MEL bindings for the RenderMan standard, it also becomes possible to insert RenderMan commands anywhere during rendering (see MEL RenderMan Binding). This is the equivalent of “RIB Boxes” in other softwares but with the added flexibility of a scripting language. In addition to insert points listed here, there are others available in Geometry Attribute Nodes (see Geometry MEL Scripts) and in the Light Attribute Nodes (see Light MEL Scripts).
The variable 'string $render_pass' is automatically defined in the context of these scripts and is assigned the current Render Pass node name.
The MEL Scripts group
Pre Render MEL
Post Render MEL
Specify scripts to run before the rendering starts and after the rendering is finished, respectively. Those scripts are guaranteed to run first and last. They are also executed outside of any RiBegin/RiEnd block, so these scripts are not appropriate for invoking RenderMan commands.
Pre Frame MEL
Post Frame MEL
Specify scripts to run before and after each frame, respectively. These two scripts are the very first and last things executed for each frame; they are called even before and after the RiBegin/RiEnd block, so these scripts are not appropriate for invoking RenderMan commands.
Post Option MEL
Specifies a script to execute after all RenderMan options have been issued, but before the camera transforms. This can be used to override any options.
Pre World MEL
Specifies a script to execute just before RiWorldBegin which is also right after where the camera transforms are issued.
Post World MEL
Specifies a script to execute right after RiWorldEnd (but before RiFrameEnd).